#494 imapproxy: DNS RR

[Wolfgang Breyha]

This patch adds support for DNS RR. In case you have several IMAP Frontends available via DNS round robin you can add
dns_rr yes
to your configfile. Currently without any retrymechanisms.

It also adds support to limit the DNS lookup to a specific IP Version by setting
ipversion_only 4|6
which sets AF_INET(6) for getaddrinfo().

The patch also touches some syslog messages to be formatted like others.

[Paul Lesniewski]

Accepted. Thank you!